This research is concerned with the influence of environmental stress on blood pressure control mechanisms using young adult humans and chronically instrumented dogs. Work over the past year has demonstrated (1) Stressors resulting in active coping, e.g., an avoidance task, more consistently evoke beta-adrenergic influences on the heart and vasculature and hence cardiac control of blood pressure than stressors resulting in more passive involvement, e.g., inescapable pain. The latter evoke primarily increases in peripheral resistance and hence vascular control of blood pressure. (2) Aortic dP/dt has been shown to be a sensitive index of sympathetic influences on left ventricular performance. (3) Beta-adrenergic influences on the heart have a more appreciable effect on systolic blood pressure than vascular influences. (4) Work now in progress indicates that when beta-adrenergic influences on the heart are evoked - the resulting increase in cardiac output is excessive relative to increases in oxygen consumption as measured by artio-venous oxygen differences. (5) Pulse wave velocity is being evaluated in humans as to its sensitivity to depict beta-adrenergic influences on the heart. (6) Humans considered to have a labile or borderline hypertension are being evaluated as to their reactivity, both cardiac and vascular, to active and passive stressors. Bibliographic references: Lawler, J.E., Obrist, P.A. and Lawler, K.A. Cardiovascular functions during pre-avoidance, avoidance and post-avoidance in dogs. Psychophysiology, 1975, 12, 4-11; Howard, J.L., Gaebelein, C.J., Galosy, R.A. and Obrist, P.A. Effects of neuromuscular blocking drugs in cats on heart rate changes to direct neural stimulation and during classical conditioning. Journal of Comparative and Physiological Psychology, 1975, 88, 868-877.